Contact cooled electronic enclosure

ABSTRACT

Various embodiments disclose a system and an associated method to provide cooling to a plurality of electronic components mounted proximately to one another in an electronic enclosure is disclosed. The system comprises a cold plate that is mounted on the electronic enclosure to conduct heat thermally. The cold plate has a first surface to mount proximate to the plurality of electronic components and a second surface to mount distal from the plurality of electronic components. One or more heat risers are configured to be thermally coupled between the first surface of the cold plate and at least one of the plurality of electronic components.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority benefit of U.S. Provisional ApplicationNo. 61/085,931, entitled, “A Contact Cooled Electronic Enclosure,” filedAug. 4, 2008, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present application relates generally to the cooling of compute andstorage systems; and, in a specific exemplary embodiment, to a systemand method for cooling electronic equipment in modularly deployedsystems cooled by attachment to a cold plate.

BACKGROUND

In a variety of contemporaneous applications, various types offluid-based cooling systems cool computers and other electronicequipment. In the simplest case, fluid moves heat from a hard-to-coollocation to a different area. For example, flexible fluid-filled heatpipes are employed to remove heat from hot electronic components tofinned sides of a computer case where convective cooling with ambientair removes the heat without the use of forced air.

Enterprise-based compute and storage systems are increasingly deployedas modular systems with standardized form factor electronic enclosuremodules mounted in standardized support structures. The standardizedelectronic enclosure modules can be devoted to perform any of a numberof different functions such as computing, storage, or networking. Theenclosure modules are commonly mounted in standardized supportstructures such as 19 inch (approximately 0.482 m) or 24 inch(approximately 0.610 m) wide racks. Such enclosures are commonlyindustry standard 1U (1.75 inch; approximately 4.45 cm), 2U (3.5 inch;approximately 8.89 cm), 3U (5.25 inch; approximately 13.3 cm), or 4U (7inch; approximately 17.8 cm) high. Often, the reasons for the adoptionof the larger 2U, 3U, or 4U modules are to increase reliability ofelectronic components through improved airflow for cooling and toprovide space for more adapter cards.

Modular enclosures are frequently air-cooled. The enclosures draw air infrom the room in which they are housed by means of fans that acceleratethe air and force it over the enclosure's internal components, thuscooling the components. The resulting heated air is exhausted back intothe room.

Other cooling methods have focused on fluid cooled systems using a coldplate means. The cold plate means are typically complex. For example, anindividual spring-loaded cold plate is used for each component. Eachcold plate, in turn, is connected with individual flexible pipes. Eachcold plate includes, at least, a temperature-controlled valve,temperature sensors, and controllers.

Other cooling methods have employed a compressiblethermally-conductive-material heat sink assembly. To be compressible,the heat sink assembly must conform to components to be cooled. However,all conformable materials have a relatively low thermal conductivity ascompared to pure metals or heat pipes. Thus, the conformable heat sinkassemblies have a relatively high thermal resistance. Consequently, verylittle heat spreading is provided such that each thermal interface musthave a very low thermal resistance for the assembly to be effective.Further, the assembly is not extensible to vertical daughter cards on amotherboard such as, for example, dual in-line memory modules (DIMMs)used in computer and other memory systems.

Importantly, no existing solution comprises a conventional, modularlydeployed system with a high thermal conductivity connectable to allcomponents. Further, no such system also includes high heat dissipationon a conventional motherboard, including removable daughter and memorycards, to a common cold plate. Moreover, such a system should also bereadily serviceable. Additionally, no solution proposes thermallyconnecting all such high heat dissipation devices to a common coolingplate by thermal elevation and co-planarization to a side of theenclosure. None of the existing systems further includes an easilyserviceable system accessible through a removable lid as part of theheat removal system.

BRIEF DESCRIPTION OF DRAWINGS

Various ones of the appended drawings merely illustrate exemplaryembodiments of the present invention and must not be considered aslimiting a scope of the present invention.

FIG. 1 is a cross-sectional drawing illustrating an exemplary embodimentof an enclosure with heat risers and thermal interface materials (TIMs);

FIG. 2 is a bottom and side view of an exemplary embodiment of aheat-riser/spreader made from a highly thermally-conductive materialsuch as a block of metal;

FIG. 3 is a bottom and side view of an exemplary embodiment of aheat-riser/spreader using heat pipes mounted in, for example, metalplates;

FIG. 4 is a bottom and side view of an exemplary embodiment of aheat-riser/spreader made from a flat heat pipe;

FIG. 5 is a bottom and side view of an exemplary embodiment of springheat riser;

FIG. 6 is a front and side view of an exemplary embodiment of a heatriser usable with a DIMM;

FIG. 7 is a cross-sectional drawing illustrating an exemplary embodimentof an enclosure with an auxiliary card and a motherboard;

FIG. 8 is an isometric view of an exemplary embodiment of aplanarization TIM bag; and

FIG. 9 illustrates an exemplary embodiment of a grooved interfacebetween a between heat riser and a lid.

DETAILED DESCRIPTION

The description that follows includes illustrative systems, methods, andtechniques that cover various exemplary embodiments defined by variousaspects of the present disclosure. In the following description, forpurposes of explanation, numerous specific details are set forth inorder to provide an understanding of various embodiments of theinventive subject matter. It will be evident, however, to those skilledin the art that embodiments of the inventive subject matter may bepracticed without these specific details. Further, well-knowninstruction instances, protocols, structures, and techniques have notbeen shown in detail.

As used herein, the term “or” may be construed in an inclusive orexclusive sense. Similarly, the term “exemplary” may be construed merelyto mean an example of something or an exemplar and not necessarily apreferred means of accomplishing a goal. Additionally, although variousexemplary embodiments discussed below focus on a thermal cooling systemfor electronic components, the embodiments are merely given for clarityin disclosure. Thus, any type of thermal cooling application isconsidered as being within a scope of the present invention.

Disclosed herein is a comprehensive system for adapting conventionalelectronic enclosures, components, motherboards, subassemblies, andsimilar components to conductive cooling systems. Also described hereinare methods and structures to calculate and thermally couple electroniccomponents or subassemblies housed in the conventional electronicenclosures though a side of the enclosure to a proximate cold plate. Ina specific exemplary embodiment, the cold plate comprises a lid of theenclosure. In another specific exemplary embodiment, the lid contacts anexternal cold plate therein taking at least a portion of the function ofthe cold plate itself.

The electronic components, subassemblies, or similar components arethermally elevated, planarized, and coupled, by means of heat risers andthermal interface materials (TIMs), to a side of the enclosure that, inturn, contacts a proximate cold plate. The enclosures may be the commonelectronic enclosures described above, other form-factor enclosures, orunenclosed systems such as server blades or bare server motherboards.Each of these components are known independently in the art.

The contact-cooled enclosure described herein can, among other things,comprise an instantiation of the contact-cooled enclosure referred to ina previously filed patent application by Lipp and Hughes. The patentapplication describes a rack mounted cold plate system is found in U.S.Provisional Patent Application No. 61/008,136, entitled “A CoolingSystem for Contact Cooled Electronic Modules,” filed Dec. 19, 2007, andU.S. patent application Ser. No. 12/339,583, having the same title, andfiled Dec. 19, 2008, both of which are incorporated herein by referencein their entirety.

In an exemplary embodiment, a system to provide cooling to a pluralityof electronic components mounted proximately to one another in anelectronic enclosure is disclosed. The system comprises a cold plate tomount on the electronic enclosure and thermally conduct heat. The coldplate has a first surface to mount proximate to the plurality ofelectronic components and a second surface to mount distal from theplurality of electronic components. One or more heat risers areconfigured to be thermally coupled between the first surface of the coldplate and at least one of the plurality of electronic components.

In another exemplary embodiment, a system to provide cooling to aplurality of electronic components mounted proximately to one another inan electronic enclosure is disclosed. The system comprises a cold plateto provide thermal heat conduction. The cold plate is configured to bemounted external to the electronic enclosure. One or more heat risers isconfigured to be thermally coupled on a first end to at least one of theplurality of electronic components. A lid, configured to be mounted onthe electronic enclosure, has a first surface to mount proximate to theplurality of electronic components and a second surface to mount distalfrom the plurality of electronic components. The lid has a plurality ofholes positioned to accommodate the one or more heat risers to pokethrough the lid. A layer of thermal interface material thermally couplesa second end of the one or more heat risers to the cold plate.

In another exemplary embodiment, a method for thermally coupling aplurality of heat generating components in an electronic enclosure to acold plate is disclosed. The method comprises calculating a powerdissipation of each of the plurality of heat generating components,determining an acceptable temperature rise between the cold plate andthe plurality of heat generating components, and determining anacceptable thermal impedance to maintain the acceptable temperaturerise. A surface area of the cold plate needed to conduct heat from eachof the plurality of heat generating components is calculated. A type ofheat riser selected for each of a plurality of heat risers is determinedbased on the thermal impedance where at least one of the plurality ofheat risers is associated with each of the plurality of heat generatingcomponents.

In another exemplary embodiment, an apparatus to provide cooling to aplurality of electronic components is disclosed. The apparatus comprisesa first layer of a first thermal interface material. The first thermalinterface material has a first thermal conductivity. A second layer of asecond compliant thermal interface material is joined to the firstlayer. The second compliant thermal interface material has a secondthermal conductivity being lower the first thermal conductivity. In aspecific exemplary embodiment, the first thermal interface material isjoined to the second complaint thermal interface material, forming abag. A thermally conductive fluid is encapsulated within the bag.

In a specific exemplary embodiment described herein, a system forthermally coupling one or more heat generating components in a 1Uenclosure to, for example, the removable lid of the enclosure, isdisclosed. The lid can be further coupled to an external cold plate foradditional heat removal. Although the actual descriptions providedherein are limited to 1U enclosures, a skilled artisan will recognizethat similar systems, methods, and means may be applied to other stylesof enclosures of various styles and dimensions. In addition, uponreading the disclosure, the skilled artisan will further recognize thatthe heat may be coupled to a different side of the enclosure, other thanthe lid, such as the bottom. Coupling to a different side of theenclosure can be accomplished by rearranging various elements of thevarious embodiments described.

Overview

In an exemplary embodiment, described in detail below, one or moreheat-generating components in an electronic enclosure are maintained atacceptable temperatures primarily through conduction cooling to aproximate cold plate through the lid of the enclosure. Heat is thermallycoupled from the heat generating components to heat-risers or spreaders.The heat flux may be spread out over a larger area and further coupledthrough the enclosure lid to a cold plate for heat removal. Althoughheat and heat flux are the elements of interest, for purposes herein,power and power dissipation are sometimes used as a proxy for heat flux.

In an exemplary embodiment, a methodology to design a cooling mechanismfor a given electronic component or components may start withcalculating a design window. A physical implementation of the design canuse information derived from the calculating steps.

In this exemplary embodiment, a design window can be calculated byidentifying and quantifying (e.g., calculating) a power dissipation ofall heat generating components that are not maintained at a sufficientlylow temperature by natural convection and conduction cooling means. Amaximum or acceptable temperature rise from the cold plate interface tothe heat generating components is then determined. A maximum oracceptable allowable heat flux (or power) per unit area at the coldplate/enclosure interface is determined to maintain the maximumacceptable temperature rise. The heat flux per unit area is commonlyreferred to as the thermal impedance. A cold plate surface area requiredto conduct the heat to the cold plate is calculated for each the heatgenerating components. The cold plate surface area determines an overallthermal resistance between each of the components and the cold plate.Each of these calculations and associated governing equations are knownindependently in the art.

Physical Implementation

Once preliminary calculations are determined, a distance between each ofthe one or more components and the cold plate interface is determined.An additional spatial allowance is made for one or more TIMs, generallybetween each of the one or more components and the cold plate interface.However, in certain applications, TIMs may be placed between one or moreof the components and an adjacent component as well. The one or moreTIMs can be placed in various locations, as is described below. A typeand size of each of the heat-risers or spreaders is determined based onthe heat flux, spreading information, and distances between each of theone or more components and the cold plate. The heat-risers or spreadersare produced and installed. The heat-risers or spreaders are generallyplaced to be substantially coplanar with the cold plate interface with athermally coupling between the heat-risers or spreaders between the coldplate interface with the one or more TIMs.

1U Enclosure Embodiments

A conventional motherboard is deployed in a 1U form factor electronicenclosure. The 1U electronic enclosure is nominally 1.75 inches(approximately 4.45 cm) high by 19 inches (approximately 0.482 m) wideby 24 inches (approximately 0.610 m) deep with a removable top lid inone embodiment. The enclosure may contain one or more of a computeserver, a storage device, a network switch, a power supply, otherelectronic devices, or any combination, singly or multiply, thereof.

With reference to FIG. 1, an exemplary cross-sectional view of anelectronic enclosure 100 includes a lid 111 and has a motherboard 110mounted therein. The electronic enclosure 100 and the lid 111 may eachbe fabricated from thermally conductive materials, independently knownin the art. The motherboard 110 carries some or all of the VLSIcomponents (e.g., integrated circuits in addition to discrete electroniccomponents) and most, if not all, auxiliary circuits. The motherboard110 is coupled to the electronic enclosure 100 via a plurality ofstandoffs 105. The motherboard 110 acts as a heat sink for componentsattached thereon. Through convective and radiative heat transfer to theelectronic enclosure 100, the motherboard 110 has sufficient heatdissipation to provide generally sufficient heat removal forlower-powered circuits. Heat dissipation from the motherboard 110 may befurther enhanced by one or more layers of thermal interface material(TIM) 113 arranged between the motherboard 110 and one or more walls ofthe electronic enclosure 100. The one or more layers of the TIM 113operate to bring the motherboard 110 into thermal contact with theelectronic enclosure 100. An exterior side of the lid 111 can also becovered with a thin layer of a compliant TIM 103 to optimize contactwith an external cold plate (not shown in FIG. 1).

In a specific exemplary embodiment, the compliant TIM 103 can comprisetwo layers laminated or otherwise joined together. The two layers can bejoined at or near the edges, in a quilted pattern, or in various otherfashions as will be recognizable to a skilled artisan. In this specificexemplary embodiment, the layers can be substantially comprised ofpolyester and aluminum; each layer being roughly about 0.7 mils(approximately 18 microns) in thickness. A skilled artisan willrecognize that other thicknesses and materials can be readily employed.The substantially polyester layer provides strength and toughness to thecompliant TIM 103 but the thermal conductivity is still high due to therelative thinness of the polyester layer. The substantially polyesterlayer surface also provides good thermal coupling from an external coldplate (not shown) to itself (i.e., the compliant TIM 103). The aluminumlayer spreads the heat flux coupled to the polyester layer from/to theexternal heat source/cold plate, ensuring a more uniform heat flux to aproximate thermally conductive fluid and reducing the overall thermalimpedance. In another specific exemplary embodiment, a dual-layer bagcould be formed and be further reinforced with a third lamination (notshown directly but easily understandable to a skilled artisan) forstrength, such as a porous fiberglass though which a thermallyconductive fluid could flow, thus providing additional strength whilemaintaining good thermal conductivity. A variant of this dual-layer bagis described with reference to FIG. 8, below.

Higher power dissipation devices, in particular high-density (e.g., LSI,VLSI, ULSI, etc.) integrated circuit devices such as a CPU 108, agraphics chip 109, a memory 106, a power supply transistor 114, andinductors (not shown) require heat risers to provide a low thermalimpedance path to a common plane as defined by, for example, the lid111. The heat risers conduct heat to the lid 111 from a component thatis, for example, from 0.9 inches (approximately 2.3 cm) to 1.3 inches(approximately 3.3 cm) below the lid 111. Consequently, in a specificexemplary embodiment, each of a plurality of heat risers 102, 104, 112have an overall length of from about 0.9 inches (approximately 2.3 cm)to 1.3 inches (approximately 3.3 cm). Tops of the plurality of heatrisers 102, 104, 112 are effectively planarized through the use of aplurality of riser TIMs 101 so that at least one of the plurality ofheat risers 102, 104, 112 conforms to the lid 111. Minimizing thermalimpedances from a high power dissipation device to the external coldplate (not shown) can be accomplished by spreading the heat flux over alarger area. For example, one of the plurality of heat risers 102, whichis also a heat spreader, is designed to spread the heat flux over anarea about ten times greater at its top thermal contact with one of theplurality of riser TIMs 101 to the lid 111 than at a bottom thermalcontact 107 to the CPU 108. The ten times greater area thereby reducesthe heat flux and thermal gradient across one of the plurality of riserTIMs 101, the lid 111, and the compliant TIM 103 by a factor of aboutten. The reduction in heat flux due to the greater area is more fullydescribed under VLSI cooling below. As will be recognized by a skilledartisan upon reading the disclosure, a heat riser may be used to carrythe heat away from more than one component. For example, one of theplurality of heat risers 102 is also in thermal contact with the powersupply transistor 114, transporting heat generated therein, along withheat from the CPU 108 to the lid 111.

Thermal paths for high dissipation, high heat flux integrated circuitdevices (e.g., devices fabricated according to VLSI or ULSI designprinciples) are provided by combination heat-risers/spreaders. Suchheat-risers/spreaders have top surfaces from about two to twenty timeslarger than their bottom surfaces. For example, with reference now toFIG. 2, one of the plurality of heat risers 102 that also has heatspreading characteristics, is examined in further detail. In anexemplary embodiment, at least one of the plurality of heat risers 102is constructed from a highly thermally conductive material, such as ametal block.

In a specific exemplary embodiment, the metal block is fabricated fromaluminum. In this specific exemplary embodiment, the heat riser 102 is 3inches (approximately 7.6 cm) wide by 6 inches (approximately 15.2 cm)long by 1 inch (approximately 2.5 cm) high. A pad area 202 is configuredto mount to the CPU 108. The heat riser 102 receives heat from a highheat flux area of the pad area 202 and spreads the heat flux(illustrated by a plurality of dashed arrows 204) over a larger area 203to reduce the heat flux. A surface area of the larger area 203 is about10 times larger than a surface area of the pad area 202, thus reducingheat flux proportionately (i.e., by a factor of ten). Reducing the heatflux allows use of thermal interface materials with lower thermalconductivity, while still maintaining a thermal resistance from theelectronic component through the lid 111 (or another side of theelectronic enclosure 100) of less than about 0.25° C./Watt.

The heat riser 102 is installed in contact with the VLSI component, suchas the CPU 108, using the same fixtures as are normally used to holddown a conventional heat sink. In this specific exemplary embodiment,two screws 205 secure the heat riser 102 to the VLSI component.

In other specific exemplary embodiments, the heat riser 102 can beconstructed using a simple block of a conducting material such asaluminum or graphite. Each of these, and related materials, may bemachined or cast into more complex shapes to optimize performance perunit weight, to fit into limited areas, or to contact multiple heatgenerating components. Alternately, the heat riser 102 may be fabricatedfrom more complex constructs using, for example, heat pipes.

Referring to FIG. 3, another exemplary embodiment of a heat riser 102 auses a plurality of heat pipes 301. The plurality of heat pipes 301 maybe tubular or solid round, square, or various other shapes and can befabricated from highly thermally conductive material such as, forexample, copper. The plurality of heat pipes 301 are thermally coupledwith two or more parallel plates (only two plates are shown for clarity)including a small plate 302 and a large plate 303. The small plate 302and the large plate 303 can be fabricated from any highly thermallyconductive material, such as copper. The small plate 302 is intended forplacement on top of the device to be cooled, such as the CPU 108, andthe large plate 303 can be placed against the lid 111 of the electronicenclosure 100 (see FIG. 1).

The plurality of heat pipes 301 is arranged so that their centersections are in good thermal contact with the small plate 302 and eachof the ends of the plurality of heat pipes 301 are arranged in goodthermal contact with the large plate 303. In a specific exemplaryembodiment, thermal contact with both the small plate 302 and the largeplate 303 is augmented by placing each of the plurality of heat pipes ingrooves (not shown explicitly but understandable to a skilled artisan)milled into the small plate 302 and the large plate 303. The grooves areroughly equal in diameter to each of the plurality of heat pipes 301. Inanother specific exemplary embodiment, each of the plurality of heatpipes 301 is affixed by soldering. Using the design and fabricationtechniques described herein, the heat riser 102 a has a thermalresistance of less than about 0.07° C./Watt.

A total number of the plurality of heat pipes 301 and dimensions of thesmall plate 302 and the large plate 303 can be adapted to fit variousapplications. The larger the large plate 303 in relation to the smallplate 302, the greater the reduction in heat flux across the large plate303. In a specific exemplary embodiment, the small plate 302 hasdimensions of about 2 inches by 2 inches (approximately 5.1 cm square)and the large plate has dimensions of about 6 inches by 3 inches(approximately 15.2 cm by 7.6 cm). As the device to be cooled, such asthe CPU 108 (see FIG. 1) has a top surface of about 1.3 inches by 1.3inches (approximately 3.3 cm square), the generated heat flux iseffectively spread over an area about ten times greater at the largeplate 303 as compared to the small plate 302.

The plurality of heat pipes 301 could be replaced by a single wide flatheat pipe (not shown, but understandable to a skilled artisan). Takingit a step further as illustrated in an exemplary embodiment of FIG. 4,the small 302 and the large 303 plates of FIG. 3 can be eliminated andsubstituted by a flat, wide heat pipe 401. The flat, wide heat pipe 401may be used as a heat-riser/spreader all by itself. The flat, wide heatpipe 401 is fabricated from a highly thermally conductive material suchas metal (e.g., copper). In a specific exemplary embodiment, the flat,wide heat pipe 401 is 3 inches (approximately 7.6 cm) wide and placed sothat its center portion lies directly on top of the device to be cooled,such as the CPU 108, and a large portion of the ends of the flat, wideheat pipe is in contact with the lid 111 of the electronic enclosure 100(see FIG. 1). Compared to the heat pipe/riser/spreader described abovewith reference to FIG. 2, thermal performance is slightly better withthe flat, wide heat pipe 401 and a lack of coplanarity between thecomponent (e.g., the CPU 108) and the lid 111 can be compensated for bythe flexibility of the heat pipe. In other exemplary embodiments (notshown), the flat, wide heat pipe 401 can be used in conjunction with theplurality of heat pipes 301 of FIG. 3.

Heat Risers

In the various exemplary embodiments disclosed above, each of the risersalso spreads the heat over a larger area. For components that dissipateless heat than various ones of the high-density integrated circuitsdiscussed above, simpler risers can sufficiently be effective forcooling the components. For example, a simple block heat riser havingdimensions of 1 inch by 1 inch by 1 inch (approximately 2.5 cm on aside) can be fabricated from aluminum. Since any face in contact with acomponent has an opposing face, to be thermally coupled to the lid 111,has as identical surface area, no heat spreading occurs.

With reference to FIG. 5, an exemplary embodiment of one type ofeffective heat riser is a spring riser 500 as illustrated. The springriser 500 is similar to one of the plurality of heat risers 104 of FIG.1 and the flat, wide heat pipe 401 of FIG. 4. The spring riser 500 canbe constructed out of a highly thermally conductive flexible materialsuch as, for example, copper. The spring riser benefits from beingfabricated from an at least slightly resilient material, such as copper,to provide a spring-like characteristic to the spring riser 500.

In a specific exemplary embodiment, the spring riser 500 can be a roundor elliptical spring having a width 506 of about 1 inch (approximately2.5 cm) wide and a thickness 505 of about 5 mils (0.005 inches orapproximately 127 microns). However, various shapes other than round canreadily be employed as well as other dimensions.

The spring riser 500 removes heat from a component, such as the graphicschip 109 of FIG. 1, by a combination of conduction to the lid 111, andnatural convective and radiative heat transfer to a local environment ofthe component. The spring riser 500 can be affixed to the component bygluing or other means, and has at least one of a plurality of riser TIMs101 thermally coupling the spring riser 500 to the lid 111. Thespring-like nature of the spring riser 500 assures a good mechanical andthermal contact to the lid 111, while automatically compensating forvariations in height and coplanarity. The spring riser 500 is light inweight and low in cost. Thermal resistance for an exemplary embodimentof the spring riser 500 described above ranges from about 0.5° C./Wattto 2° C./Watt.

Referring now to FIG. 6, various types of volatile and non-volatilememory subassemblies, such as VRAM or DRAM dual in-line memory modules(DIMMs), can be cooled by conductive heat transfer. In an exemplaryembodiment, a DIMM 606, is encased with one or more thermally conductivestrips 612 on its sides that act as heat risers. The one or morethermally conductive strips 612 make thermal contact to memorycomponents 613 within the DIMM 606 at a thermal interface 607. Thethermal interface 607 can be a thermally conductive grease knownindependently in the art. Thus, the thermal interface 607 can be athermal-grease-based TIM.

Vertical sides of the one or more thermally conductive strips 612provide a low thermal impedance path from the DIMM 606 to an uppermostportion 614 of the one or more thermally conductive strips 612. In aspecific exemplary embodiment, a 1 mm thick aluminum block is used forthe one or more thermally conductive strips 612. The one or morethermally conductive strips 612 can be held in place by, for example, aplurality of spring clips 611.

In an alternative exemplary embodiment, the one or more thermallyconductive strips 612 can be glued to components of the memorycomponents 613 without requiring the plurality of spring clips 611. Theglue thus provides both a mechanical and thermal attachment.

The uppermost portion 614 of the one or more thermally conductive strips612 is substantially orthogonal to the sides and made as wide as a pitchof the DIMM 606 allows (e.g., 0.4 inches or approximately 10 mm), thusminimizing the thermal resistance of the DIMM 606 to an interface of thelid 111 of the electronic enclosure 100 (see FIG. 1). A typical thermalresistance of the interface between the DIMM 606 and the lid 111 is 1.6°C./Watt with 0.2 mm thick TIM. Generally, a worst case thermalresistance is 2° C./Watt for the exemplary embodiment shown, resultingin a temperature rise of approximately 20° C. for a 10 Watt DIMM.

Note that although the one or more thermally conductive strips 612 areshown on both sides of the memory subassembly, in many cases componentsare mounted on one only side. Thus, in such an application only thesingle mounted side requires only one of the one or more thermallyconductive strips 612.

In a specific application of various embodiments of thermally coolingelectronic components described herein, a voltage regulator module (VRM,not shown) converts an internal 12 V power supply to voltages requiredby the individual components, such as the CPU 108 and the memory 106(see FIG. 1). The VRM often supplies over 100 amps of current at justover 1 VDC and dissipates up to 30 Watts. In contemporaneous designs,the power is commonly dissipated among six transistors and inductors.

Most server designs have the VRMs built onto the motherboard with theinductors and switching transistors laid out in a row up to 4 inches(approximately 10 cm) long. Consequently, a generated heat flux isrelatively low. A piece of metal such as 4 inch long by ⅛ inch thick(approximately 10 cm long by 3.2 mm thick) aluminum strip (not shown) isplaced over the transistors and inductors with a thin thermal interfacecoating there-between. The piece of metal can, in turn, be coupled tothe lid 111 of FIG. 1 by one of the plurality of heat risers 102 asshown for the power supply transistor 114, or a solid metal, such as theheat riser 102 a of FIG. 3, or one of the spring risers, such as flat,wide heat pipe 401 or the spring riser 500, of FIGS. 4 and 5respectively, can be employed to thermally rise and couple the aluminumstrip to the lid 111.

In another specific application of various embodiments of thermallycooling electronic components described herein, an input power converterconverts input power to a lower intermediate voltage, nominally 12 VDC.Power is delivered to a motherboard through one or more electricalconnectors. Input power converter subassemblies are mounted (not shown),typically by screws, directly to the lid 111 of the electronic enclosure100. A layer of thermal interface material between the cover and thedevice ensures good thermal contact.

In another specific application of various embodiments of thermallycooling electronic components described herein, disk drives (not shown)consume about 10 Watts so adequate cooling is typically achieved byconductive and natural convective heat transfer within an enclosure.Cooling of the disk drives can be enhanced by inserting, for example, aTIM 113 such as was done for the motherboard 110 of FIG. 1 between thedisk drive and the electronic enclosure 100.

In another specific application of various embodiments of thermallycooling electronic components described herein, auxiliary circuit boardsubassemblies generally have low dissipation (e.g., below 30 Watts) andjust a few integrated circuit components. With reference to FIG. 7, in a1U-sized system, an auxiliary circuit board 701 is commonly insertedinto the motherboard 110 so that the auxiliary circuit board 701 iscoplanar with and slightly above the motherboard 110 as illustrated.Components mounted to the auxiliary circuit board 701 can be cooled viaan aluminum block or a spring riser 704 glued, coupled, or otherwiseadhered on top of the components and coupled to the lid 111 of theelectronic enclosure 100 in a fashion similar to that described forother devices, above.

Further, a plurality of auxiliary circuit boards (not shown explicitly)can be placed in an area previously occupied by fans and associatedcontrol mechanisms normally used for forced-air convective cooling. Theplurality of auxiliary circuit boards can be connected to themotherboard with high speed interfaces such as HyperTransport®, PCIExpress®, or any other similar widely accepted protocol. Mounting theplurality of auxiliary circuit boards in an area previously occupied byfans and associated control mechanisms enables a 1U enclosure to offerthe same functionality as a 2U, 3U, or 4U enclosure.

Other objects, such as the auxiliary circuit board subassembliesdescribed immediately above, may obstruct a direct thermal path betweenthe motherboard 110 component and the lid 111. In such a case, heatgenerated by the component are directed around the obstruction. Forexample and with continuing reference to FIG. 7, a component, such asthe graphics chip 109, no longer has a direct unobstructed path to thelid 111. The auxiliary circuit board 701 (plugged into a socket 702)lies directly above the graphics chip 109. In this case, an exemplaryhalf spring riser 703 has one end in thermal contact with the graphicschip 109, wraps around the auxiliary circuit board 701, and thermallycontacts at least one of the plurality of riser TIMs 101 under the lid111. For medium and lower power devices, the half spring riser 703 canbe a simple strip of copper as described above for one of the springrisers, such as the spring riser 500 of FIG. 5. If a lower thermalresistance is required, the half spring riser 703 can be constructedmuch like the flat, wide heat pipe 401 described with reference to FIG.4.

Alternatively, the half spring riser 703 can be fabricated from aheavier gauge thermally-conductive material or even a block of metal cutin such a fashion as to extend out from under the obstruction and riseto the lid 111. In another exemplary embodiment, a TIM (not shown) maybe inserted under the obstructed component in order to conduct heat tothe enclosure bottom as referred to above. The variations described arenot all not shown as they are too numerous to itemize and are readilyapparent to one skilled in the art using the disclosure and embodimentsprovided herein.

Heat Riser Planarization

After thermal risers are attached to many or all components within theelectronic enclosure 100, thus bringing the thermal risers nominally upto a level of a lower portion on the underside of the lid 111, aplanarization step can be included further enhancing thermal coupling tothe lid 111 with a low thermal resistance.

Assembly of the motherboard 110 may result in the top portions of thecomponents not being coplanar either with one another or an uppermostportion of heat risers attached thereto not being coplanar with thelower portion of the underside of the lid 111. Consequently, the upperportions of the attached heat risers may not be at an exact distancebelow the lid 111. For example, an integrated circuit may havedimensions of 33 mm×33 mm with an installed height variance of roughly0.2 mm, and a surface coplanarity variance of about 0.3 mm betweeneither of the two sets of parallel faces. A top face or surface of, forexample, the larger area 203 of one of the plurality of heat risers 102(see FIG. 2), multiplies an effect of the variation simply due to theincreased surface area. Moreover, both the motherboard 110 and theelectronic enclosure 100 are flexible and can sag away from theirrespective support structures. In this example, coplanarity variance canbe up to roughly 1.4 mm or more.

While any of the various spring risers described herein are flexible,and will therefore adjust to variations in height and planarityautomatically, the tops of larger risers/spreaders (e.g., one of theplurality of heat risers 102) can benefit from planarization and aresulting height adjustment thus assuring good, low-thermal resistancecoupling to the lid 111. Ordinary rubber-like TIM sheet materials of theprior art do not have sufficient compliance to overcome largecoplanarity differences.

Several methods may be employed to offset a lack of coplanarity. In anexemplary embodiment, a compliant thermally conductive substance, suchas a thermal grease, known independently in the art, can improveconductive heat transfer between contacting surfaces. Additionally, aself-leveling thermally conductive potting compound may be poured in amask over the riser and allowed to set. In another exemplary embodiment,a thermal grease or thermally conducting potting compound may beencapsulated in a bag and laid over one or a plurality of risers,functioning as at least one of the plurality of riser TIMs 101. The bagof this exemplary embodiment is described in detail with reference toFIG. 8, below. Self-leveling thermally conductive potting compounds areknown independently in the art.

In a specific exemplary embodiment, an uppermost top portion of the heatriser 102 is covered with a moderately high conductivity (e.g., 3Watts/m-°K) potting compound prior to replacing the lid 111 on theelectronic enclosure 100. The potting compound is cured in place betweenthe heat riser 102 and the lid 111. The cured potting compound thenfunctions as at least one of the plurality of riser TIMs 101 describedabove with a thermal impedance of less than about 0.1° C./Watt/in²(approximately 0.016° C./W/cm²).

Further, since contacting surfaces between the top of risers/spreadersand the underside of the lid 111 are never perfectly flat or coplanar,and may even be non-rigid and flexible, thermal grease or an elastomericpad (known separately and independently in the art), may be insertedbetween the contacting surfaces. Alternatively or in addition, the risermay be physically clamped to the lid by a screw or clamping fixture, orotherwise adhered (e.g., by an epoxy or chemical bonding agent), using agenerally inherent flexibility of the motherboard 110 and the lid 111 tocompensate for non-coplanarity and height variations. The flexibility ofthe motherboard 110 can compensate for some or all the height andcoplanarity issues. After mounting the heat riser 102 on the componentto be cooled and replacing the lid 111, the heat riser 102 is clamped tothe lid 111 in order to draw the heat riser 102 against it. Thermalresistance is minimized by flattening the heat riser 102 against the lid111 and minimizing a thickness of one or more of the plurality of riserTIMs 101. Screwing or locking sliders (not shown but readily understoodby a skilled artisan) are one form of attachment but other attachmentmethods will work. The clamping process can benefit from a rigidenclosure lid capable of remaining relatively flat when force is appliedthereto. The heat riser 102 is lifted into contact with the rigid lidand the motherboard 110 is flexed to compensate for any mechanicalheight differences due to, for example, dimensional tolerances of thevarious components such as the lid, motherboard, heat riser, etc.).

In another exemplary embodiment, any of the risers or spreaders arepatterned (not shown but readily understandable to a skilled artisan) onan uppermost portion (i.e., that portion configured to contact the lid111). A portion of the lid 111, corresponding to a contact point of thepatterned riser or spreader, is similarly patterned to engage with theriser or spreader pattern. The patterned surface increases an overallsurface area of the contacting surfaces, thus increasing the thermalcontact area. Patterning of opposing surfaces brought into contact withone another is discussed in more detail with reference to FIG. 9, below.

In another exemplary embodiment, a compliant thermally-conducting foam(not shown) can function as at least one of the plurality of riser TIMs101. The compliant thermally conducting foam is compressed by the lid111 providing coplanarity between the heat riser 102 and the lid 111.The compliant thermally conducting foam is useful in situations whereplanarity divergence is small or relatively high pressures can beapplied to press down the lid 111.

In yet another exemplary embodiment, a flexible vapor chamber (notshown) fabricated from a resilient and thermally conductive material canbe clamped to the riser or device to be cooled. A pressure-cooker-effectis then utilized to expand a top of the vapor chamber top into planaritywith the lid 111, thus providing enhanced conductive heat transfer. Askilled artisan will recognize that any or all of the methods and meansdescribed above can be combined for various applications.

With reference now to FIG. 8, a bag 801, discussed briefly above, isfilled with a self-leveling thermally conductive fluid 802 (note thatthe thermally conductive fluid 802 is contained within the bag 801). Thefluid can be, for example, a thermal grease. Various types of thermalgrease are known independently in the art. For a single riser, the bag801 can be fabricated to be slightly larger than a top surface of theriser, for example, from about 5% to 20% larger on a side. For example,for the 3 inch by 6 inch (approximately 7.6 cm by 15.2 cm) dimension ofthe larger area 203 of the heat riser 102 (see FIG. 2) discussed above,the bag can be 3.3 inches by 6.6 inches (approximately 8.4 cm by 16.8cm). The bag 801 can be sized large enough to allow an excess amount ofthe thermally conductive fluid 802 a place to escape when the fit istight, but not so large that much of the thermally conductive fluid 802will flow away beyond one or more edges of the heat riser 102, thusleaving a void above the heat riser 102. An amount of the thermallyconductive fluid 802 used in the bag 801 is dependent upon a worst-casecoplanarity variation, as described above. The bag 801 could also belarge enough to cover a multiplicity of components, simply covering overmany or all of the components. In another exemplary embodiment, the bag801 can act as the lid 111 of the electronic enclosure 100.

In a specific exemplary embodiment, the bag 801 can be fabricated usinga dual-layer polyester and aluminum construction. This embodiment isdescribed with reference to the specific exemplary embodiment ofconstructing the compliant TIM 103 discussed above. For the bag 801, thedual-layers can be filled with various types of fluid such as thethermally conductive fluid 802. In a related specific exemplaryembodiment, one of the layers of the bag can be the lid 111 of theelectronic enclosure 100. The second of the dual-layers is coupled tothe lid 111 so as to form a cavity between the lid 111 and the second ofthe dual-layers. The second of the dual-layers can be comprisedsubstantially of either, for example, aluminum or polyester. In thiscase, the bag 801 can be in contact with one surface of the entire lid111 or, alternatively, in contact with only certain portions. Of course,multiple instantiations of the bag 801 can be in contact with differentareas of the lid 111 as well. Additionally either of the dual-layers canbe comprised of any other material that is generally non-reactive whenin contact with the thermally conductive fluid 802 or thermal greasesand has a relatively good thermal conductivity. Additionally, thematerials for the dual-layers should be relatively impervious to leakswhen used to encapsulate various types of fluid such as the thermallyconductive fluid 802. In other exemplary embodiments where the bag 801comes into contact with the lid 111, there should be a good thermalcontact between the bag 801 and the lid 111.

In another exemplary embodiment, the bag 801 can be fabricated using adual-layer polyester and aluminum construction on one side with theother side comprising the lid 111 of the electronic enclosure 100 (seeFIG. 1). The dual-layer polyester and aluminum construction side isaffixed to the lid 111 by gluing or other means. This embodiment isdescribed with reference to the specific exemplary embodiment ofconstructing the compliant TIM 103 discussed above. For the bag 801, thespace between the dual-layers and the lid 111 can be filled with varioustypes of fluid as the thermally conductive fluid 802.

The thermally conductive fluid 802 can either be a setting ornon-setting compound depending upon a specific application. For example,if components within the electronic enclosure 100 are changed over thelife of the equipment, a non-setting compound is adaptable to the newdimensions of one or more new components. However, a setting compound isless likely to leak or otherwise fail than a non-setting compound. Thus,the setting compound can be better suited for applications that are notmodified.

In a specific exemplary embodiment, the bag 801 is utilized to achievethe pressure-cooker effect, describe above. This specific exemplaryembodiment is similar to the aforementioned technique of encapsulatingthermal grease or thermally conducting potting compound in a bag.However, with the pressure-cooker effect, the bag 801 is fabricated froma flexible and thermally conductive material. The bag 801 is evacuated,except for a small amount of the thermally conductive fluid 802 thatboils just above the cold plate operating temperature. The bag 801,acting as a vapor chamber, is affixed to the heat riser 102. When thebag 801 cools, it is compressed flat by the lack of vapor-counteractingair pressure. When the heat riser 102 starts to conduct heat, the bag801 warms up until the thermally conductive fluid 802 boils, expandingthe bag 801 and forcing it tightly against the lid 111. At that point,the thermally conductive fluid 802 at the top of the bag 801 that is inthermal contact with the lid 111 cools and condenses, thus releasingheat into the lid 111. In this manner, heat is transferred from the heatriser 102 to the lid 111.

Referring now to FIG. 9, an exemplary embodiment of a grooved interfacebetween the heat riser 102 and the lid 111 exemplifies one of thetechniques described above to compensate for a lack of coplanarity. Inthis exemplary embodiment, the heat riser 102 is patterned with aplurality of grooves 901. The plurality of grooves 901 engages aplurality of corresponding grooves 902 formed into a lower portion ofthe lid 111.

In a specific exemplary embodiment, each of the plurality of grooves 901and the plurality of corresponding grooves 902 are formed to a depth of3 mm with a groove pitch 903 of 1 mm, along the z-axis (the z-axis beingdefined as being orthogonal to the drawing), such that a width of each“tooth” is slightly less than one half the groove pitch 903. This ratioassures some skew tolerance in the x-axis as well as the y- and z-axes.However, the width of the teeth can vary between the plurality ofgrooves 901 and the plurality of corresponding grooves 902 or even fromtooth-to-tooth. The only requirement is that the two components properlymate such that a surface area, and a resulting convective heat transfer,increases. When the lid 111 is replaced, the two sets of grooves meshand, because of the skew tolerance, compensation is made between a lackof coplanarity between the heat riser 102 and the lid 111.

The grooved surfaces thus assure a larger interface area for a lowerthermal resistance between the heat riser 102 and the lid 111. Thegrooved surfaces may be manufactured as part of the heat riser 102 andthe lid 111, or they may be separate pieces of thermally conductivematerial applied to either or both surfaces. To further increaseconvective heat transfer between the mating surfaces, either thermalgrease is applied between the surfaces to effect a low thermalresistance or one or both surfaces can include a compliant and thermallyconductive TIM. Using the teachings herein, one skilled in the art willrealize other depths, pitches, and interlocking patterns other thangrooves, (e.g., a checkerboard pattern), may also be used in differentapplications.

Lid Modifications and Lidless Enclosures

In the various embodiments described herein, heat risers are used as athermal path between one or more of the various components to be cooledand an enclosure lid. In an exemplary embodiment, to properly coupleheat from the top of the heat riser to the cold plate through the lidutilizes, for example, at least two of the plurality of riser TIMs 101or the compliant TIM 103 as shown in FIG. 1. In high power applications,such as a 200-Watt CPU, or when it is desirous to have the temperaturedifference between the component and the cold plate lower, the twolayers of TIM may add too much thermal resistance. In such a case, thelid may be modified or eliminated.

In the first case where the lid is modified, holes are cut through thelid to match sizes of one or more of the heat-risers or spreaders. Theheat-risers/spreaders are made slightly taller than described in otherembodiments, above, so the heat-riser/spreaders poke through the lid andare level with an outside portion of the top of the lid. A single layerof TIM is then added to the top of the riser that is then directlycoupled to an external cold plate through this single TIM layer.

In the second case where the lid is completely eliminated, the bag 801of FIG. 8 above is designed to fit over the top of all the heat risercomponents, thereby replacing and eliminating the lid. In applicationswhere the lid is used for other purposes, such as Faraday shielding forEMI, the bag 801 can be metalized and electrically coupled to theenclosure to provide for electrical isolation. This technique is alsoapplicable to blade servers. Moreover, to spread heat better across thelid, the lid itself, or a portion thereof, may be constructed as a flatheat pipe or vapor chamber using techniques described above.

Although various embodiments have been described herein, it will beevident that various modifications and changes may be made to theseembodiments without departing from the broader spirit and scope ofvarious forms of the present invention. Accordingly, the specificationand drawings are to be regarded in an illustrative rather than arestrictive sense. The accompanying drawings that form a part hereofshow by way of illustration, and not of limitation, specific embodimentsin which the subject matter may be practiced. The embodimentsillustrated are described in sufficient detail to enable those skilledin the art to practice the teachings disclosed herein. Other embodimentsmay be utilized and derived therefrom, such that structural and logicalsubstitutions and changes may be made without departing from the scopeof this disclosure. The Detailed Description, therefore, is not to betaken in a limiting sense, and the scope of various embodiments isdefined only by the appended claims, along with the full range ofequivalents to which such claims are entitled.

Such embodiments of the inventive subject matter may be referred toherein, individually or collectively, by the term “invention” merely forconvenience and without intending to voluntarily limit the scope of thisapplication to any single invention or inventive concept if more thanone is, in fact, disclosed. Thus, although specific embodiments havebeen illustrated and described herein, it should be appreciated that anyarrangement calculated to achieve the same or similar purposes may besubstituted for the specific embodiments shown. This disclosure isintended to cover any and all adaptations or variations of the variousembodiments. Combinations of the above embodiments, and otherembodiments not specifically described herein, will be apparent to thoseof skill in the art upon reviewing the above description.

For example, particular embodiments describe various arrangements,dimensions, materials, and topologies of systems. Such arrangements,dimensions, materials, and topologies are provided to enable a skilledartisan to comprehend principles of the present disclosure. Thus, forexample, numerous other materials and arrangements may be readilyutilized and still fall within the scope of the present disclosure.Additionally, a skilled artisan will recognize, however, that additionalembodiments may be determined based upon a reading of the disclosuregiven herein.

1. A system to provide cooling to a plurality of electronic componentsmounted proximately to one another in an electronic enclosure, thesystem comprising: a cold plate to thermally conduct heat and beingconfigured to mount on the electronic enclosure, the cold plate having afirst surface to mount proximate to the plurality of electroniccomponents and a second surface to mount distal from the plurality ofelectronic components; and one or more heat risers, each of the one ormore heat risers having a first end configured to be thermally coupledto the first surface of the cold plate and a second end to be thermallycoupled to at least one of the plurality of electronic components. 2.The system of claim 1, further comprising a thermal interface materialconfigured to be thermally coupled between at least one of the one ormore heat risers and the first surface of the cold plate.
 3. The systemof claim 1, wherein the electronic enclosure is a standard 1U type ofelectronic enclosure.
 4. The system of claim 1, wherein the cold plateis fabricated from a thermally conductive material and forms a lid forthe electronic enclosure.
 5. The system of claim 1, wherein at least oneof the one or more heat risers having a first surface to thermallycouple to at least one of the plurality of electronic components, thefirst surface having a first surface area, the at least one of the oneor more heat risers having a second surface to thermally couple to thecold plate, the second surface having a second surface area that islarger than the first surface area.
 6. The system of claim 5, whereinthe second surface area is from about two to twenty times larger thanthe first surface area.
 7. The system of claim 1, wherein a thermalresistance between the plurality of electronic components and the coldplate is less than about 0.25° C. per Watt.
 8. The system of claim 1,wherein each of the one or more heat risers has an overall length fromabout 2.3 cm to 3.3 cm.
 9. The system of claim 1, wherein at least oneof the one or more heat risers is fabricated from a plurality of heatpipes affixed to a first thermally conductive plate and a secondthermally conductive plate, the first thermally conductive plate beingthermally coupled to each end of the plurality of heat pipes and thesecond thermally conductive plate being thermally coupled to anotherportion of the plurality of heat pipes.
 10. The system of claim 1,wherein at least one of the one or more heat risers is fabricated from aflat heat pipe affixed to a first thermally conductive plate and asecond thermally conductive plate, the first thermally conductive platebeing thermally coupled to each end of the flat heat pipe and the secondthermally conductive plate being thermally coupled to another portion ofthe flat heat pipe.
 11. The system of claim 1, wherein at least one ofthe one or more heat risers is a spring riser fabricated from a flexiblethermally conductive material.
 12. The system of claim 11, wherein thespring riser has a thermal resistance within a range of about 0.5° C.per Watt to about 2° C. per Watt.
 13. The system of claim 1, wherein thecold plate is a bag filled with thermally conductive fluid.
 14. Thesystem of claim 13, wherein the thermally conductive fluid is aself-leveling fluid.
 15. The system of claim 13, wherein the bag ismetalized to provide EMI shielding.
 16. The system of claim 1, furthercomprising a thermally conducting potting compound to be applied betweenthe one or more heat risers and the cold plate.
 17. The system of claim16, wherein the thermal impedance of the thermally conducting pottingcompound is less than about 0.016° C./W/cm².
 18. The system of claim 1,further comprising a self-leveling thermally conductive fluidencapsulated within a bag, the bag being configured to provide a thermalinterface and planarization structure over at least one of the one ormore heat risers.
 19. The system of claim 18, wherein a portion of thebag to be thermally coupled with the at least one of the one or morerisers has an area from about 5% to 20% a surface area of a top portionof the at least one of the one or more risers.
 20. The system of claim1, wherein the first end of the one or more heat risers is configured tobe physically adhered to the cold plate.
 21. The system of claim 1,wherein the cold plate is a flexible vapor chamber, the flexible vaporchamber being fabricated from a resilient and thermally conductivematerial.
 22. The system of claim 1, wherein the first end of at leastone of the one or more heat risers is patterned on the first end so asto engage a mating pattern on the first surface of the cold plate. 23.The system of claim 22, wherein at least one of the patterns includes athermally conductive interface material.
 24. A system to provide coolingto a plurality of electronic components mounted proximately to oneanother in an electronic enclosure, the system comprising: a cold plateto thermally conduct heat and configured to be mounted external to theelectronic enclosure; one or more heat risers configured to be thermallycoupled on a first end to at least one of the plurality of electroniccomponents; a lid configured to mount on the electronic enclosure, thelid having a first surface to mount proximate to the plurality ofelectronic components and a second surface to mount distal from theplurality of electronic components, the lid further having a pluralityof holes positioned to accommodate the one or more heat risers to mounttherethrough; and a layer of thermal interface material to thermallycouple a second end of the one or more heat risers to the cold plate.25. A method to thermally couple a plurality of heat generatingcomponents in an electronic enclosure to a cold plate, the methodcomprising: calculating a power dissipation of each of the plurality ofheat generating components; determining an acceptable temperature risebetween the cold plate and the plurality of heat generating components;determining an acceptable thermal impedance to maintain the acceptabletemperature rise; calculating a surface area of the cold plate toconduct heat from each of the plurality of heat generating components tothe cold plate; and selecting a type for each of a plurality of heatrisers based on the thermal impedance, at least one of the plurality ofheat risers being associated with each of the plurality of heatgenerating components.
 26. The method of claim 25, further comprising:determining a distance between each of the plurality of heat generatingcomponents and a proximate surface of the cold plate; planarizing eachof the plurality of heat risers to be substantially coplanar with theproximate surface of the cold plate; and thermally coupling theplurality of heat risers to the cold plate.
 27. The method of claim 26,further comprising coupling the plurality of heat risers to the coldplate by placing a thermal interface material therebetween.
 28. Anapparatus to provide cooling to a plurality of electronic components,the apparatus comprising: a first layer of a first thermal interfacematerial, the first thermal interface material having a first thermalconductivity; a second layer of second compliant thermal interfacematerial, the second compliant thermal interface material having asecond thermal conductivity being different than the first thermalconductivity, the second layer being joined to the first layer.
 29. Theapparatus of claim 28, wherein the first layer joined to the secondlayer forms a cavity, and a thermally conductive fluid is encapsulatedwithin the cavity.
 30. The apparatus of claim 29, further comprising athird porous layer fabricated between the first layer and the secondlayer to provide strength to the apparatus, the third porous layerfurther configured to allow the thermally conductive fluid to movetherethrough.
 31. The apparatus of claim 28, wherein the first layer issubstantially comprised of aluminum and the second layer issubstantially comprised of polyester.
 32. The apparatus of claim 28,wherein the thermally conductive fluid is a self-leveling fluid.
 33. Theapparatus of claim 28, wherein the bag is metalized to provide EMIshielding.
 34. The apparatus of claim 28, wherein each layer of the bagis approximately 18 microns in thickness.
 35. The apparatus of claim 28,wherein the first layer is a lid of an electronic enclosure.
 36. Theapparatus of claim 28 further comprising a layer of thermal grease to beplaced on an external surface of one or both of the first layer and thesecond layer prior to thermally coupling the apparatus between one ormore of the plurality of electronic components and a cold plate.
 37. Anapparatus to provide cooling to a plurality of electronic components,the apparatus comprising: a layer of a compliant thermal interfacematerial, the compliant thermal interface being configured to thermallycouple to a lid of an electronic enclosure and form a cavity between thelid and the layer of the complaint material; and a thermally conductivefluid configured to be encapsulated within the cavity.
 38. An apparatusto provide cooling to a plurality of electronic components, theapparatus comprising a thermal interface material comprising at leasttwo layers, the two layers including a first layer and a second layer,the first layer being configured to provide strength to the apparatusand thermally couple to at least one of the plurality of electroniccomponents, the second layer being configured to thermally spread heattransferred from the at least one of the plurality of electroniccomponents.
 39. The apparatus of claim 38, wherein the first layer issubstantially comprised of polyester and the second layer issubstantially comprised of aluminum.